by Liz Szabo, USA TODAY

by Liz Szabo, USA TODAY

Taking testosterone therapy doubled the risk of heart attack among men over age 65 and nearly tripled the risk in younger men with a history of heart disease, a new study shows.

The report, which involved 56,000 men, is the latest in a series of studies raising concerns about the heart attack risk from testosterone therapy, whose popularity has ballooned in recent years. The study was published Wednesday in PLOS One.

Francisco Lopez-Jimenez, a cardiologist at the Mayo Clinic in Minnesota not involved in the new study, describes the heart risks posed by testosterone therapy as substantial.

"That's equivalent to smoking one or two packs of cigarettes a day, or having sky-high cholesterol," Lopez-Jimenez says.

Authors of the study, led by researchers at the University of California-Los Angeles and others, say doctors should discuss these risks with patients. Testosterone is often called the "male hormone" because it causes development of male sex organs, facial hair and other masculine features.

Drug companies also have marketed testosterone directly to consumers, however, urging men to consider hormones to treat the symptoms of "low T," which are said to include energy loss, mood changes and reduced sex drive.

Those ads appear to have been hugely successful.

Doctors wrote more than 5.3 million prescriptions for testosterone therapy in 2011, five times as many as in 2000, according to a November report in the Journal of the American Medical Association. The number of men taking testosterone tripled from 2001 to 2011, with the drugs now used by nearly 4% of men in their 60s, according to a separate study last year in JAMA Internal Medicine.

Yet only about half of men taking testosterone therapy had been diagnosed with hypogonadism, and 25% hadn't even had their testosterone levels tested, according to the JAMA Internal Medicine study. The rest of patients had been diagnosed with other problems such as fatigue or sexual dysfunction.

A spokesman for AbbVie, which makes AndroGel, one of the most popular testosterone therapies, notes that studies also have found health benefits from the medications. A 2012 study linked testosterone with a lower risk of death. A 2013 study in the Journal of Clinical Practice found that men taking the therapy long-term had healthier cholesterol levels, blood sugar levels and blood pressure.

"We encourage discussion between physicians and patients that leads to proper diagnosis based on symptoms, lab tests and a patient's other health needs," says David Freundel, a spokesman for AbbVie.

Abraham Morgentaler, an associate clinical professor of urology at Harvard Medical School, says it's possible that the men's heart attacks in this study were caused by their underlying medical problems, not by testosterone. He notes that most heart attacks occurred in the first 90 days after a prescription was written. It's unlikely that heart attacks could develop in such a short period of time, he says.

Nissen, chair of cardiovascular medicine at the Cleveland Clinic, notes that hormones have powerful and sometimes surprising effects throughout the body, not just on sexual organs. He cited hormone replacement therapy, which was once touted as a way to prevent heart disease in women but was later found to cause heart attacks, strokes and breast cancer. Prescribing testosterone therapy to thousands of men who may not really need it, he says, is "a "gigantic experiment, and I'm extremely concerned."